Year years 1960 43.993486357175584 1961 44.274597971699215 1962 44.72700321049756 1963 44.95898203137488 1964 45.46666422028322 1965 45.578930199343404 1966 45.61956927750423 1967 45.69978400546966 1968 46.129198146610555 1969 46.2533660713396 1970 46.749806984342804 1971 47.376194394539155 1972 47.410074732442865 1973 48.022916589638044 1974 48.18447447386702 1975 48.35053525156468 1976 48.81282397826332 1977 49.30665371070862 1978 49.37630316139985 1979 49.637572973958214 1980 49.80575053531591 1981 49.905808946970026 1982 49.78598498401338 1983 49.26043192155872 1984 49.009751268056036 1985 49.24260011787955 1986 49.84187389028516 1987 50.221502781604606 1988 49.7846322220983 1989 50.91501429063781 1990 50.91116173177179 1991 51.03457423372003 1992 51.040660017270945 1993 51.43377713332655 1994 52.165338854236325 1995 51.815945406943115 1996 51.89583540938624 1997 52.20749324250528 1998 51.91186202261232 1999 52.652252769590405 2000 53.47936261453365 2001 53.74635483632314 2002 54.154940844522244 2003 54.391849081524434 2004 54.6448705416865 2005 55.010821683735294 2006 55.51032887037098 2007 55.973876771752884 2008 56.14065186934741 2009 57.10888011920211 2010 57.427193397876025 2011 58.04399700940767 2012 58.199426047075534 2013 58.43947798454929 2014 58.65528667477789 2015 58.95171518584268 2016 59.17742008525795 2017 59.52656542504803 2018 59.8236347881128 2019 60.142066000069924 2020 59.587721179492235 2021 59.03943971154157 2022 59.58385589822264